The aim of this project is to establish the steric course of the formation of 1-aminocyclopropane-1-carboxylic acid (ACC) from S-adenosyl-methionine (SAM) by ACC synthase and the steric course of the ring opening of ACC to 2-ketobutyric acid (2-KB) by ACC deaminase. Regio- and stereo-specific isotopically labeled SAM's and ACC's will be used to gain information concerning the mechanism of these two pyridoxalphosphate (PLP)-containing enzymes whose catalyses are unique variations in PLP-assisted Gamma-elimination-addition type reactions. The total steric course of each enzyme reaction will be elucidated from the sum of the individual stereo-chemical events occurring at the Alpha, Beta, and Gamma carbons of each substrate amino acid. Both enzymatic and chemical methodology will be utilized to synthesize the regio and sterospecific 13C- and 2H-labeled SAM's. The configuration of the enzymatic products (ACC and 2-KB) will be determined using a combination of the following: 1H- and 13C-nmr, mass spec., neutron diffraction analysis, ORD and CD. A secondary aim is to explore the steric course of the enzymatic oxidation of ACC to ethylene employing both the chirally labeled ACC's as well as the methodology developed above.